1. Field of the Invention
This invention relates generally to fluorescent lamp systems and more particularly to such systems wherein the lamp is operated at a high frequency by means of control logic and power switching devices which are located on a single integrated circuit chip.
2. Description of the Prior Art
Fluorescent lamps require a ballast circuit because fluorescent lamps have a negative resistant characteristic. As current flowing through the lamp increases, voltage across the lamp decreases. Eventually, the lamp will act like a short circuit if the current is not limited in some way.
A ballast circuit acts to limit current flowing through the lamp. The typical ballast circuit operates at line frequency (sixty hertz) and is primarily just a large inductor. This simple type of ballast circuit has been used with fluorescent lamps for many years. It does however have some disadvantages. The large inductor makes the circuit heavy and bulky. It is also inefficient because fluorescent lamps operate at optimum efficiency at higher frequencies in the range of twenty-five kilohertz to fifty kilohertz.
Prior art systems have been made which operate fluorescent lamps in this higher frequency range. However, the complexity of these systems has made them highly unreliable and costly compared with the simple inductor ballast systems. Even though the lamp operates more efficiently, the energy savings has not been enough to off-set the initial high cost of these lamp systems and thus, they have not been economically viable. Examples of such systems include U.S. Pat. No. 4,170,746, issued to J. Davenport; U.S. Pat. No. 4,544,862, issued to H. Yamazaki, et al.; U.S. Pat. No. 4,220,895, issued to E. Nuver; and U.S. Pat. No. 4,306,177, issued to I. Kaneda.
Various federal and state codes have been passed recently which call for more efficient lighting. There is a need for an efficient and low cost fluorescent lamp system.